ENTAMOEBA HISTOLYTICA 35 



amoebae ; since the erring individuals are unable to complete their 

 development, and are thus inevitably lost to the species as a whole. 



Other life-histories of £. histolytica have been described, but they 

 appear to rest upon misinterpretations of various sorts. The more 

 important of these will be considered later. I would note particularly 

 here, however, that there is no " spore-formation " such as Schaudinn 

 (1903) described in this species, and that " schizogony," or multiple 

 fission, does not occur ; and further, that no conjugation or other sexual 

 process has yet been shown to take place at any stage in the life-history. 



The chief points in the habits and life-history, as outlined above, will 

 now be considered in further detail. 



Habitat. — The normal habitat of E. histolytica, as already noted, is 

 the tissue of the large intestine* of man. The parasites are here found 

 in the mucous, submucous, and occasionally the muscular layers, where 

 they cause a typical ulceration. I need not here discuss the morbid 

 anatomy of the various forms of intestinal amoebiasis. Good descrip- 

 tions are to be found in the publications of Councilman and Lafleur 

 (1891), Dopter (1905, 1907), Kuenen (1909), Christoffersen (1917), and 

 others, to whose works the reader may be referred. 



The commonest secondary site of infection is the liver, where the 

 parasites give rise to the formation of abscesses. There can be little 

 doubt that they reach this organ by way of the portal vein. From the 

 liver they may pass in the blood stream to the lungs, brain, and possibly 

 other organs, where they may also settle down and cause the formation 

 of abscesses. Amoebic abscess of the brain is a very uncommon disease, 

 only about 50 cases having been recorded.f Amoebic abscesses in the 

 spleen have been described by J. P. Maxwell (1909) and Rogers (1913), 

 and infections of the urinary system may occur.J I have studied several 

 cases of liver abscess and specimens from one cerebral abscess — thanks 

 to my friend Capt. L. Armitage, N.Z.M.C. — and I can confirm the 

 observations of many other workers that the amoebae in these situations 

 are indistinguishable from the forms in the gut wall. The pathological 

 anatomy of these various lesions does not concern us here. 



E. histolytica has been stated by Lesage (1907) to occur at times in 

 the blood ; in the skin, by various workers (cf. p. 140) ; and in other 

 situations. The evidence for such statements is, however, still far from 

 convincing. Job and Hirtzmann (1919) have recently alleged that 

 E. histolytica {"Amoeba dysenteriae") is intracellular during its youngest 

 stages of development in the liver. But their account is too brief and 

 unconvincing to overthrow all the observations of other workers — none 

 of whom have ever found truly intracellular stages of this parasite. 



Mode of Nutrition. — A study of sections of intestinal ulcers and liver 

 abscesses, and of the amoebae themselves as they occur in fresh 

 dysenteric stools, makes it abundantly clear that E. histolytica nourishes 

 itself at the expense of the tissues. The amoebae penetrate the tissues 

 by destroying the cells. In all probability they do not force their way 

 mechanically into the healthy tissues, but secrete a powerful cytolytic 



* Infection of the small intestine by E. histolytica is extremely rare. It has been 

 described by Harris (1898) and Kuenen (1909) in man, and I have seen two instances 

 in the cat (cf. Dale and Dobell, 1917)- 



+ See especially Legrand (1912), Sitsen (1913), and Armitage (1919). 



J Cf. p. 125 et seq. 



